Tools to monitor immune cell interactions and their consequences will accelerate development of successful immunotherapies for cancer, HIV disease, and autoimmune disorders. High levels of autofluorescence and spectral overlap limit use of stable fluorescent labels for cell proteins or membranes with other visible probes. High levels of tissue absorption and scattering preclude real time optical imaging in intact animals. PTIR has synthesized five new cell tracking dyes fluorescing in the 667-837 nm range (far red - near infrared). S/N for labeled cells were up to 15x of those for PKH26; spectral overlap properties were suitable for use with many other fluorescent probes; and feasibility criteria for chemical stability, photostability, and lack of effect on cell viability and growth were met. Labeled cells were also readily imaged in superficial lung microvessels using intact organ microscopy and at subcutaneous injections sites in nude mice, attesting to the potential for noninvasive, whole body imaging. In Phase II PTIR will develop two kits f or preclinical use and screening and initiate studies to support a clinical cell tracking dye. The first kit will be for standard 3-4 color instruments, the second for high-end instrumentation. Our collaborators will evaluate both kits by monitoring proliferation of lymphocyte subsets, determining the depth to which tumor cells can be tracked in intact lung preparations from rats, and determining the minimum number of cells which can be imaged at deep vs. superficial sites in intact animals. PROPOSED COMMERCIAL APPLICATION: Membrane labeling dyes emitting in the far red or near infrared have significant commercial potential in three markets; 1) a research market serving both basic and clinical investigators using flow cytometers; 2) a similar and rapidly growing market in optical imaging, especially intact organ or whole body imaging; and for molecules with suitable photochemical properties, 3) photodiagnosis and/or phototherapy.